DE69023299T2 - Cored wire for welding stainless steel. - Google Patents

Description

Background of the invention Field of the invention

The invention relates to the use of a flux cored wire for welding stainless steel and, in particular, to the use of a flux cored wire which is applicable under the same conditions to welding operations in all positions, including not only upright, sideways, vertical and horizontal fillet welding operations, but also overhead welding operations, and which is capable of forming a weld metal with excellent properties in terms of welding process and X-ray properties.

State of the art

Due to their practicality, coupled with high efficiency and quality, the demand for flux-cored wires (FCW) has recently increased significantly, even in stainless steel welding processes. However, their application has so far been mostly limited to normal position and horizontal welding operations and to parts of welding operations in horizontal and vertical positions, with practically no applications encountered in operations in overhead positions.

More specifically, stainless steels, which have lower thermal conductivity and solidification temperatures compared to carbon steel, require higher welding techniques in the horizontal and vertical welding positions, where drops of molten metal occur more easily than in the upright welding position. In particular, in overhead welding, it has been difficult to obtain practically satisfactory X-ray properties, even when using specially designed power sources and shielding gas.

Under these circumstances, various attempts have been made to meet the growing need for a flux cored wire that enables welding in all positions. For example, flux cored wires of this type proposed in Japanese Patent Publication 59-15757 and Japanese Laid-Open Patent Application 59-212192.

The first-mentioned Japanese Patent Publication No. 59-15757 describes a wire intended mainly for horizontal and vertical position welding, while Japanese Patent Application Laid-Open No. 59-212192 discloses a filler wire applicable to welding operations in the normal position, horizontal and vertical positions, although the welding conditions differ greatly between the normal position and vertical positions. Besides, these prior art wires require low-current welding conditions in the vertical position compared with the normal position position. Accordingly, in a case where a welding operation includes all welding positions in its sequence, it becomes necessary to use different wires in the normal position and vertical (or horizontal) positions, or to use one wire under different conditions. More specifically, in the vertical welding position, despite a significant drop in efficiency, it becomes necessary to use a current that is about 50% lower than in the upright welding position; the need for weaving also makes it difficult to obtain weld beads with short weld legs, coupled with the problem that the wire is only applicable to plates with a thickness greater than 5 mm and not to plates with a smaller thickness. Moreover, in the case of upright welding in the vertical position, the operation often becomes impracticable due to unstable arc conditions and drops of molten metal that destabilize the weld pool.

Therefore, due to problems in controlling welding operations or problems in the efficiency of welding in vertical position, conventional flux cored wires (FCW) have found only limited use and, therefore, overhead welding operations have so far been based on arc welding with coated electrodes or TIG welding without the use of FCW.

US-A-4,366,364 discloses a filler wire for use in gas shielded arc welding. The welding medium includes the following:

Metal fluoride as fluorine 0.025-0.35 (wt.%)

Metal carbonate ≤0.5

1 or more selected from the group consisting of Al, Ti, Zr, V and Ca ≤0.75

TiO2 3.5-7.4

SiO₂ ≤ 2.0

MgO and/or ZrO2 0.03-1.2

Al₂O₃ ≤0.15

C ≤ 0.15

Mn1.2-3.0

Si 0.3-1.2

Summary of the invention

In view of these situations, the object of the invention is to provide a flux cored wire for use in welding stainless steel which can be used in all welding positions including the overhead position with improved handling and under the same conditions and which can form a weld metal with good properties including X-ray properties, etc.

Common flux cored wires for use in welding stainless steel in most cases use a flux of the TiO₂-SiO₂-ZrO₂ system to which appropriate amounts of Al₂O₃, MgO, MnO₂ and the like are added for adjusting the viscosity and slag solidification temperature.

The cored wires of this type have the following problems:

(1) It is difficult to use them especially in a welding operation with all positions including the overhead position and to ensure satisfactory handling in all welding positions;

(2) the dripping of molten metal can be suppressed by increasing the content of slag-forming components in the wire to generate a large amount of slag as in gas-shielded arc welding; however, such an increase in the content of slag-forming components causes a significant deterioration of the X-ray properties;

(3) the welding conditions must be varied depending on the welding position, e.g. vertical and overhead positions where welding with high current is impracticable, coupled with difficulties in normal position welding in vertical position due to the need for weaving.

To solve these problems, the inventor has conducted an extensive study to find an optimum wire composition by optimizing the amount of slag production, solidification temperature and viscosity from the viewpoint of maintaining excellent arc stability and concentration over a wide range of welding conditions, particularly taking into account the differences in optimum physical properties between the overhead and normal position welding positions.

The present invention has been accomplished based on the finding that the above-mentioned problems are solved by using a welding agent of a TiO₂-Al₂O₃ system containing Al₂O₃ as a main component and rich in TiO₂, ensuring an optimal balance of TiO₂, Al₂O₃, SiO₂ and/or ZrO₂ components and limiting the amount of metal fluorides, and adding Ti and limiting the amounts of slag-forming agent and preferably (Al₂O₃ + SiO₂ + ZrO₂).

Namely, according to the invention, the use of a filler wire for welding stainless steel is provided, wherein the wire comprising a welding agent filled in a stainless steel sheath and wherein the welding agent contains, based on the total weight of the wire, 8.5 - 13.5% slag-forming components comprising, based on the total weight of the wire, 4.7 - 8.5% TiO₂, 0.5 - 3.5% Al₂O₃ and 0.6 - 3.0% SiO₂ and/or ZrO₂ in proportions satisfying the following formula:

TiO2; > Al₂O₃ + SiO2 + ZrO2;

and in addition 0.03 - 0.25% metal fluoride (expressed as F- conversion value) and 0.1 - 1.0% Ti. The welding fluid contains essentially no CO₂ or carbonate.

According to another aspect of the invention, the proportions of the slag-forming components satisfy the following formula

Al₂O₃ + SiO2 + ZrO2; ≤ 5.0%.

The above and other objects, features and advantages of the invention are set forth in claims 3 to 10 and will become apparent from the following specific description and appended claims taken in conjunction with the accompanying drawings.

Short description of the drawing

In the following drawing:

Fig. 1(a) to 1(d) are cross-sectional views showing, by way of example, a number of cored wires; and

Figures 2 and 3 are diagrammatic views of the shapes of compounds used in examples that will appear hereinafter.

Specific description of the invention

According to the invention, the respective welding agent components are each contained within the above-mentioned limited ranges for the following reasons. From this point of view, it is important to note that the desired effect or effects discussed below are not caused by one welding agent component alone, but synergistically by a number of components contained in the welding agent composition in balanced proportions.

(1) Optimization of TiO₂�min;, Al₂O₃�min;, SiO₂�min; and ZrO₂ contents

TiO₂ as a slag forming component has the effect of improving slag coverage and slag flaking and as an arc stabilizing agent has the effect of improving arc concentration and suppressing spatter. However, a TiO₂ content of less than 4.7% is not sufficient to ensure this effect, while a On the contrary, a content of more than 8.5% facilitates deterioration of the slag coverage and impairs the bead appearance and X-ray properties. Accordingly, the TiO₂ content should be in the range of 4.7 - 8.5% based on the total weight of the wire, preferably in the range of 5.8 - 8.2%.

Al₂O₃ is a main component of the welding agent system according to the invention and, as a slag-forming component, has the effects of increasing the slag solidification temperature without changing its viscosity, in addition to the effect of improving slag flaking. MgO and ZrO₂ also serve to raise the solidification temperature, but are not suitable as a main component in view of the change in slag viscosity that would be caused by them. An Al₂O₃ content of less than 0.5% is not sufficient to achieve the desired effects, while a content of more than 3.5% results in deteriorated X-ray properties. Accordingly, the content of Al₂O₃ should be in the range of 0.5 - 3.5% based on the total weight of the wire, preferably in the range of 0.7 - 2.7%.

SiO₂ and ZrO₂, which as slag-forming components exhibit effects of improving slag coverage and increasing slag viscosity to improve weld bead shape, are added individually or together. A content of SiO₂ and ZrO₂ of less than 0.6% is insufficient to achieve the intended effects, while a content of more than 3.2% results in a weld bead of defective convex shape and deteriorated X-ray properties. Accordingly, the content of SiO₂ and/or ZrO₂ should be in the range of 0.6 - 3.2% based on the total weight of the wire, preferably in the range of 1.0 - 3.0%.

However, the welding agent components described above should be added in proportions that meet the conditions of the following formula:

TiO2; > Al₂O₃ + SiO2 + ZrO2;

Fulfilling this condition is essential to optimize slag solidification temperature and viscosity, improve arc stability and concentration, and broaden the range of suitable conditions to enable welding operations in all positions under the same conditions.

(2) Metal fluorides

The metal fluoride is an essential component for improving the anti-porosity property (X-ray properties), and has the effect of regulating the fluidity of the slag. It is important to determine the amount of metal fluoride added so that it is in balance with the other slag-forming components such as TiO₂. A metal fluoride content of less than 0.02% is not sufficient to ensure the intended effects, while a content of more than 0.25% results in increased levels of moisture and spatter. Accordingly, the content of metal fluoride should be in the range of 0.02 - 0.25%, expressed as the value of F-conversion based on the total weight of the wire, preferably in the range of 0.02 - 0.15% from the viewpoint of weldability (particularly slag coverage).

(3) Addition of Ti

As an arc stabilizer, Ti has the effects of improving arc concentration and reducing spatter. In addition, as a deoxidizer, Ti has the effect of improving X-ray properties.

Ti, which is in easily fusible form, acts as a slag forming agent by melt oxidation, which is of even greater importance.

In the case of a FCW with an excess content of an oxidic slag-forming component, the welding current flows only through the sheath part of the wire, which prevents the melting of the internal welding agent which has a higher melting point than a metal is delayed, thereby causing unmelted welding agent residues to deteriorate X-ray properties. Accordingly, the proportion of slag-forming components in the wire has a limit. On the other hand, the slag-forming components must be added in a large amount to prevent dripping of the molten metal in vertical and overhead welding positions. According to the present invention, to solve this problem, the wire of the present invention contains TiO₂ and Al₂O₃ in appropriately balanced proportions which are free from unmelted residues, while TiO₂ is added as a main component in a metallic form which hardly causes unmelted residues. Easily fusible Ti forms TiO₂ by melt oxidation, which participates in slag formation to prevent dripping of molten metal. However, a Ti content of less than 0.1% is not sufficient to achieve the desired effect, while a Ti content of more than 1.0% increases spatter in the normal welding position and results in defective weld bead shape and undercut.

Therefore, the Ti content should be in the range of 0.1 - 1.0% based on the total weight of the wire, preferably in the range of 0.3 - 0.8%. Ti can be added in the form of metallic titanium or ferrotitanium.

Although the invention has been described in terms of the essential points, it is desirable to add the following limitations, if necessary, in order to broaden the range of applicable conditions in all welding positions, particularly in vertical and overhead welding positions, and to realize higher current welding positions.

(4) Content of slag-forming components & (Al₂O₃ + SiO₂ + ZrO₂)

The content of slag-forming components must be 8.5% or greater to prevent dripping of molten metal.

However, unmelted residues of the slag-forming components occur if their content is greater than 13.5%, which impairs the X-ray properties. Accordingly, the content of slag-forming agent should be in the range of 8.5 - 13.5% based on the total weight of the wire, preferably in the range of 9.0 - 13.5%.

In addition, from the viewpoint of arc stability and concentration at high current and improvement of X-ray properties, it is desirable to keep the content of (Al₂O₃ + SiO₂ + ZrO₂) 5.0% or less based on the total weight of the wire, preferably in the range of 1.1 - 5.0%.

In addition, in view of the importance of arc concentration (intensity), particularly in vertical and overhead welding of thin plates, it is desirable to set the ratio of Ti/F (converted) to a value greater than 3.8 inclusive. This will make the impingement of molten drops at a given current, particularly in the overhead welding position, stronger, thereby enabling straight wire movements and ensuring excellent weldability. On the contrary, if the ratio of Ti/F exceeds 30, the intensification of arc impingement achieved in the vertical and overhead welding position will become too strong in the upright position and cause spatter to an objectionable degree. Therefore, the ratio of Ti/F should be less than 30.

With regard to optional additives other than the above-mentioned components, appropriate amounts of the following substances may be added, provided that they do not substantially contain CO₂ or a carbonate.

The welding consumable may in fact be enriched with appropriate amounts of: MgO, MnO or similar to fine-tune the physical properties of the slag; Bi₂O₃ to improve slag exfoliation; Na or K to improve arc stability; and Ni, Cr, Mo, Mn, Si, Nb, C, N, Fe, Al, V, W, Cu or similar to adjust the weld metal composition.

The metal sheath of the wire is made of stainless steel, which is not subject to any particular restrictions as to its composition, and has a composition determined depending on the intended use. For example, it can be a ferritic or austenitic stainless steel. There are no restrictions on the section of the wire, which can have any of the shapes shown as examples in Fig. 1.

The invention is illustrated more specifically by the following examples.

[Examples]

The cored wires of Tables 2 and 3 were prepared using 0.7 mm (D) x 12 mm (B) stainless steel casings of the chemical compositions shown in Table 1. In these tables, the amounts of the filler metal components are given as a percentage of the total weight of the wire, and the amounts of metal fluoride are expressed as F-conversion values.

The respective wires were examined by welding test in different positions under the conditions given in Table 4.

The welding test was carried out with a welding operation including upright, vertical and overhead positions for a butt joint as shown in Fig. 2 and a horizontal fillet welding operation as shown in Fig. 3. In the case of the joint of Fig. 2, the test was carried out by multiple welding using a backing B, plates of a thickness T of 16 mm, a bevel angle θ of 60º, a route face F of 1 mm and a route gap (G) of 3 mm. In the case of the joint of Fig. 3, the test was carried out by single welding using plates of a thickness T.

The plates used in the tests were stainless steel plates as specified in JIS G4304 or G4305 and of a composition equal to that of the wires used.

The results of the welding tests are shown in Tables 5 and 6, in which the classification of quality is indicated by (extremely good), o (good), Δ (slightly defective) and X (defective); the determination of the X-ray properties was carried out according to JIS Z 3106.

As is clear from Table 6, the examples of the invention can all be welded in all positions and have excellent quality combined with satisfactory X-ray properties.

On the other hand, the comparative examples shown in Table 5 are mostly not suitable for all-position welding, and the X-ray properties are inferior even if the quality of all-position welding is satisfactory (No. 9). Table 1 - Chemical composition of the shell metal Metals Table 4 - Welding conditions Welding conditions Normal position Welding-Vertical Positions-Overhead Horizontal-Fill weld Current (A) Voltage (V) Speed (cm/min) Note: Wire diameter: 1.2 mm Power source: DC source Shielding gas: CO₂, 20 1/min Table 2 Wire No. Metal Cover Welding Fluid Composition Slag Forming Components Metal Fluorides Total Metal Components Remarks Note 1: The metal fluoride contents are given by F transformation values. Note 2: The Ti contents in "Fe-40%Ti" are given by Ti transformation values. Table 3 Wire No. Metal cover Welding agent composition Slag forming components Metal fluorides Total metal components Remarks Note 1: The metal fluoride contents are given by F-conversion values. Note 2: The Ti contents in "Fe-40%Ti" are given by F-conversion values. * Comparative examples Table 5 Wires No. Functionality All positions Arc stability Arc concentration Slag flaking Normal position Spraying Bead appearance Bead shape (solid state) of deposited metal) Vertical Spraying Overhead X-ray properties (grade) Normal position Overall rating Remarks All lower than grade 3 All not usable Comparison examples Table 6 Wires No. Functionality All positions Arc stability Arc concentration Slag flaking Normal position Spraying Bead appearance Bead shape (solid state) of deposited metal) Vertical Spraying Overhead X-ray properties (grade) Normal position Overall rating Remarks All not usable comparison examples

As is apparent from the above description, the invention provides a flux cored wire suitable for welding stainless steel using a TiO₂-Al₂O₃ system flux containing Al₂O₃ as a main component and rich in TiO₂, with an appropriate balance of TiO₂, Al₂O₃, SiO₂ and and/or ZrO₂ contents are ensured and the content of metal fluoride is limited, or Ti is additionally added, or the content of slag forming agents and (Al₂O₃ + SiO₂ + ZrO₂) is limited to enable all-position welding including the overhead position without changing the welding conditions from one position to another, while ensuring excellent welding quality to form a weld metal with favorable X-ray properties. In addition, the wire used in the invention has advantages in that vertical and overhead position welding operations are possible with the same high current as in the normal position position, and that straight wire tracking is possible in up- or normal position welding positions in the vertical position, thereby enabling formation of beads with short weld legs and application to thin plates.

Claims (10)

1. Use of a filler wire for welding stainless steel, wherein the wire comprises a welding agent filled in a stainless steel sheath, and wherein the welding agent contains, based on the total weight of the wire, 0.1 - 1.0% Ti, 8.5 - 13.5% slag-forming components and contains substantially no CO₂ or carbonate, wherein the slag-forming components comprise, based on the total weight of the wire, 4.7 - 8.5% TiO₂, 0.5 - 3.5% Al₂O₃ and 0.6 - 3.2% SiO₂ and/or ZrO₂ in ratios satisfying the following formula: TiO2; > Al₂O₃ + SiO2 + ZrO2; and also contains 0.02 - 0.25% metal fluoride (expressed as F-conversion value). 2. Use according to claim 1, wherein the slag-forming components include Al₂O₃, SiO₂ and ZrO₂ in ratios satisfying the following formula: Al₂O₃ + SiO2 + ZrO2; ≤ 5.0%. 3. Use according to claim 1 or 2, wherein the welding agent contains 5.8 - 8.2% TiO₂ based on the total weight of the wire. 4. Use according to one of claims 1 to 3, wherein the welding agent contains 0.7 - 2.7% Al₂O₃ based on the total weight of the wire. 5. Use according to one of claims 1 to 4, wherein the welding agent contains 1.0 - 3.0% SiO₂ and/or ZrO₂ based on the total weight of the wire. 6. Use according to one of claims 1 to 5, wherein the welding agent contains 0.02 - 0.15% metal fluoride (in F-conversion value) based on the total weight of the wire. 7. Use according to one of claims 1 to 6, wherein the welding agent contains 0.3 - 0.8% Ti based on the total weight of the wire. 8. Use according to one of claims 1 to 7, wherein the ratio Ti/F (F conversion value) is in the range of 3.8 ≤ Ti/F ≤ 30. 9. Use according to claim 2, wherein the welding agent contains 9.0 - 13.5% slag-forming components based on the total weight of the wire. 10. Use according to claim 2, wherein the welding agent contains Al₂O₃, SiO₂ and ZrO₂ in the range of 1.1 - 5.0% based on the total weight of the wire.